Liquid waste, i.e., wastewater, which contains mainly water and organic and inorganic materials as the remainder, has been generated in all industrial fields including petrochemical industry and also in consumer product fields. Liquid waste containing for example organic matters or hazardous substances, which cannot be discharged out directly, should be subjected to a detoxification treatment. Out of detoxification treatments, high temperature oxidation, i.e., an incineration treatment, where a wastewater is combusted at a high temperature by feeding it into a combustion furnace (burning furnace), has been known and used frequently, because a large amount of wastewater can be treated. A gaseous waste, i.e., waste gas, is also treated alone or together with the wastewater in a similar manner.
As disclosed in Patent Document 1, the applicant had proposed, in a combustion method for processing such a waste, to elongate the lifetime of a refractory lined to an internal wall of a combustion furnace by circulating a heat transfer medium such as dibenzyl toluene or polymeric oil in an external wall region of the furnace so that the temperature of the medium and the temperature of an internal surface of the furnace are controlled. Precisely, in the combustion method, the external wall region of the furnace has a jacket structure allowing the circulation of the heat transfer medium described above. Then, by controlling the temperature of the heat transfer medium to cool the internal wall of the furnace, the surface temperature of the internal wall can be adjusted within an appropriate range. By doing so, fused alkali salts derived from alkali components in the waste can be coated so as to form a self-protecting film on the surface of the refractory lined to the internal wall of the furnace. Thus, corrosion of the refractory lined there is prevented so as to elongate the lifetime of the refractory.
The heat transfer medium supplied to the combustion furnace cools the refractory lined on the internal wall of the furnace so as to control the surface temperature of the refractory as described above. Due to such cooling, the heat transfer medium itself is heated and fed back from the combustion furnace. Then, the heated heat transfer medium is cooled during a flow in a circulation route to the combustion furnace to which thus cooled heat transfer medium is supplied again. In this connection, effective utilization of recovered energy of the heat transfer medium is important, because of high temperature of the heat transfer medium when it is fed back from the combustion furnace.
In the conventional combustion methods, as mentioned above, a compound as the heat transfer medium is dibenzyl toluene, polymeric oil and the like. So, it is difficult to take out such compound from a combustion system for utilization of energy, thereby its application is limited. Accordingly, even if the high temperature heat transfer medium fed back from the combustion furnace is totally or partially taken out from the flow in the above circulation route within the combustion system, the taken heat transfer medium can be merely used, for example, for heat exchange with a cooling water or directly as a heat source for evaporative concentration of the waste supplied to the combustion furnace.
Then, as disclosed in Patent Document 2, the applicant proposed a combustion method and a combustion apparatus for a waste that can utilize energy generated by waste combustion more directly and efficiently for multiple purposes. In the combustion method and the combustion apparatus, a combustion furnace is cooled by supplying cooling water to an external wall of a waste combustion furnace and a heated cooling water generated by this cooling is recovered in the form of a vapor such as steam for a boiler, resulting in reliably ensured effectiveness.
Alternatively, Patent Document 3 proposes, in feeding a combustion exhaust gas from a combustion furnace into a quenching vessel containing a cooling/dissolving water and bringing the combustion exhaust gas into direct contact with the cooling/dissolving water, energy of a wet gas caused by the direct contact can be utilized effectively in combination with an absorption heat pump.